High Speed Voltage Level Shifter Circuits

ABSTRACT

A level shifter circuit for shifting a voltage level of a logic signal from a first voltage to a second voltage includes an input stage operating in a domain of a first voltage supply that receives an input signal. The input stage includes a first inverter receiving the input signal and providing a first inverted signal. An output voltage level shifting stage operating in a domain of a second voltage supply is coupled to the input stage and providing an output signal having a voltage level corresponding to the second voltage supply domain and a logic value corresponding to the input signal. The level shifter circuit enables voltage level shifting a logic signal from a high to a low operating voltage, or from a low to a high operating voltage. The level shifter circuit enables high frequency operation, providing both fast switching and low capacitance.

FIELD OF THE INVENTION

The present invention relates generally to the field of integratedcircuits, and more particularly, relates to level shifter circuits forshifting a voltage level of a logic signal from a first voltage to asecond voltage.

DESCRIPTION OF THE RELATED ART

Level shifter circuits are utilized in integrated circuits for changingthe voltage of a signal from a first voltage to a second voltage, suchas from a high to a low operating voltage, or from a low to a highoperating voltage. A need exists for efficient and effective levelshifter circuits. It is desirable to provide such level shifter circuitsthat enable shifting a voltage level of a logic signal from a high to alow operating voltage, or from a low to a high operating voltage.

It is desirable to provide such level shifter circuits that enableoperation between at least two different voltage domains. It isdesirable to provide such level shifter circuits that enable highfrequency operation.

It is desirable to provide such level shifter circuits that enable fastswitching and low capacitance.

SUMMARY OF THE INVENTION

Principal aspects of the present invention are to provide enhanced levelshifter circuits for shifting a voltage level of a logic signal from afirst voltage to a second voltage. Other important aspects of thepresent invention are to provide such level shifter circuits forshifting a voltage level of a logic signal from a first voltage to asecond voltage substantially without negative effect and that overcomesome disadvantages of prior art arrangements.

In brief, a level shifter circuit is provided for shifting a voltagelevel of a logic signal from a first voltage to a second voltage. Aninput stage operating in a domain of a first voltage supply receives aninput signal. The input stage includes a first inverter receiving theinput signal and providing a first inverted signal. The input stageincludes an output voltage level shifting stage operating in a domain ofa second voltage supply that is coupled to the input stage and providingan output signal having a voltage level corresponding to the secondvoltage supply and a logic value corresponding to the input signal.

In accordance with features of the invention, the level shifter circuitenables shifting a voltage level of a logic signal from a high to a lowoperating voltage, or from a low to a high operating voltage. The levelshifter circuit enables high frequency operation, for example, in aselected GHz frequency range providing both fast switching and lowcapacitance.

In accordance with features of the invention, the input stage of thelevel shifter circuit includes a second inverter receiving an invertedinput signal and providing a second inverted signal. The input stageincludes a first transistor coupled between the first voltage supply andthe first inverter receives a control input of the second invertedsignal. The input stage includes a second transistor coupled between thefirst voltage supply and the second inverter receiving a control inputof the first inverted signal. The second inverted signal is applied to afirst inverter of the output voltage level shifting stage. The firstinverter of the output voltage level shifting stage is coupled betweenthe second voltage supply and ground. A series connected P-channel fieldeffect transistor (PFET) and an N-channel field effect transistor (NFET)of the output voltage level shifting stage is connected between thesecond voltage supply VDD and ground. The first inverted signal providesan output of the output voltage level shifting stage and a gate signalto the PFET of the output voltage level shifting stage. An output of thefirst inverter of the output voltage level shifting stage provides agate signal to the NFET of the output voltage level shifting stage.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIG. 1 is a schematic diagram illustrating a first exemplary levelshifter circuit in accordance with the preferred embodiment;

FIG. 2 is a graph illustrating exemplary operation of the firstexemplary level shifter circuit of FIG. 1 in accordance with thepreferred embodiment;

FIG. 3 is a schematic diagram illustrating a second exemplary levelshifter circuit in accordance with the preferred embodiment; and

FIG. 4 is a graph illustrating operation of the second exemplary levelshifter circuit of FIG. 3 in accordance with the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with features and other advantages of the preferredembodiments, enhanced level shifter circuits for shifting a voltagelevel of a logic signal from a first voltage to a second voltage. Thelevel shifter circuits enables shifting a voltage level of a logicsignal from a high to a low operating voltage, or from a low to a highoperating voltage. The level shifters enable high frequency operation,for example, in a selected GHz frequency range providing fast switchingand low capacitance. The level shifters produce a level shifted VDDvalue with a logic value identical to the input signal, while alsomaintaining the capability of producing an output identical, butinverted from the input signal. The level shifter includes transistorsfor cutting off the flow of current between power supply domains whenthe input terminals are at a particular state.

Having reference now to the drawings, in FIG. 1, there is shown anexemplary level shifter circuit generally designated by the referencecharacter 100 in accordance with the preferred embodiment. Level shiftercircuit 100 is provided for shifting a voltage level of a logic signalfrom a first voltage to a second voltage. Level shifter circuit 100enables high frequency operation, for example, of 1 GHz frequency.

Level shifter circuit 100 includes an input stage generally designatedby the reference character 101 operating in a domain of a first voltagesupply VDD2 receiving an input signal at an input labeled IN and aninverted input signal at an input labeled INBAR. Level shifter circuit100 includes an output voltage level shifting stage generally designatedby the reference character 102 operating in a domain of a second voltagesupply VDD. Output voltage level shifting stage 102 is coupled to theinput stage 101 receiving a first inverted signal indicated at a nodeOUT_HIGH and also providing an output signal indicated at a nodeOUT_LOW. The output signal OUT_LOW has a voltage level shifted valuecorresponding to the second voltage supply VDD and a logic valuecorresponding to the input signal IN.

In accordance with features and other advantages of the preferredembodiments, the first voltage supply VDD2 optionally has a voltagelevel higher than or lower than the second voltage supply VDD.

With the first voltage supply VDD2 having a voltage level higher thanthe second voltage supply VDD, level shifter circuit 100 functions as ahigh-to-low level shifter, shifting a voltage level of a logic signalfrom a high voltage to a low voltage.

With the first voltage supply VDD2 having a voltage level lower than thesecond voltage supply VDD, level shifter circuit 100 functions as alow-to-high level shifter, shifting a voltage level of a logic signalfrom a low voltage to a high voltage.

Input stage 101 includes a pair of series connected P-channel fieldeffect transistors (PFETs) 104, 106 connected in series with a pair ofparallel connected N-channel field effect transistors (NFETs) 108, 110.PFETs 104, 106 and NFETs 108, 110 are between the first voltage supplyVDD2 and ground. A first inverter defined by PFET 106 and NFET 108receives the input signal IN and provides a first inverted signal at afirst node or net labeled OUT_HIGH. A node or net labeled A is indicatedat the drain source connection of PFETs 104, 106.

Input stage 101 includes a pair of series connected PFETs 112, 114connected in series with a pair of parallel connected NFETs 116, 118.PFETs 112, 114 and NFETs 116, 118 are connected between the firstvoltage supply VDD2 and ground. A second inverter defined by PFET 114and NFET 116 receives the inverted input signal INBAR and providing asecond inverted signal at a node or net labeled B.

Output voltage level shifting stage 102 includes a first inverterdefined by a series connected PFET 120 and an NFET 122 connected betweenthe second voltage supply VDD and ground. A second series connected PFET124 and an NFET 126 is connected between the second voltage supply VDD.The second inverted signal at net B is applied to the gate connection ofthe output stage inverter PFET 120 and NFET 122. The first invertedsignal at net OUT_HIGH is applied to the gate of PFET 124, and theinverted output of output stage inverter PFET 120 and NFET 122 isapplied to the gate of NFET 126.

Operation of the level shifter circuit 100 may be further understood asfollows. With a high or one level signal on the input IN and a low orzero level signal on the input INBAR, net A being the drain of PFET 104is pulling high compliment of the source connected to the first powersupply VDD2.

Net B output of inverter PFET 114 and NFET 116 gates PFET 104, NFET 110,PFET 112, and NFET 122 pulling in the direction of the input signal IN,while connected to the drains of NFETs 116, 118 and PFET 114. The inputsignal IN is applied to the gates of inverter PFET 106 and NFET 108 thatinverts the input signal, and maintains a high level at output netOUT_HIGH as dictated by the power supply VDD2 on source of PFET 104.

This inverted signal at output net OUT_HIGH is maintained by being tiedto the gates of PFETs 124, 112 and NFET 118. Net C provides drain-sourceconnection for PFETs 112, 114 respectively, following in the directionof the inverted input signal INBAR. The inverted input signal INBAR isapplied to the second inverter PFET 114, NFET 116 and is inverted asidentified by net B and then shifted down to the target VDD by theoutput stage inverter PFET 120, NFET 122. The level shifter signal isnow held low and maintained by NFET 126. PFETs 120, 124, NFETs 122 and126 together shift this signal to the shifted voltage level.

FIG. 2 illustrates exemplary operation of the level shifter circuit 100in accordance with the preferred embodiment, where the first voltagesupply level VDD2 in this case is 2.7V and is shifted down to the secondvoltage supply level VDD which is 1.3V. In FIG. 2, time is shown innanoseconds along the horizontal axis and voltage is shown along thevertical axis in volts (V). An exemplary input signal is indicated by INand an exemplary output signal at node OUT-LOW is indicated by OUT-LOW.

Referring now to FIG. 3, there is shown another exemplary level shiftercircuit generally designated by the reference character 300 inaccordance with the preferred embodiment. Level shifter circuit 300 isprovided for shifting a voltage level of a logic signal from a firstvoltage to a second voltage, and is arranged for providing highfrequency operation. Level shifter circuit 300 enables high frequencyoperation, for example, of 1.5 GHz frequency, higher than level shifter100 while level shifter circuit 100 has the advantage of requiring fewercomponents.

Level shifter circuit 300 includes a first input stage generallydesignated by the reference character 301 operating in a domain of afirst voltage supply VDD2 receiving an input signal at an input labeledIN and an inverted input signal at an input labeled INBAR. Level shiftercircuit 300 includes a first output voltage level shifting stagegenerally designated by the reference character 302 operating in adomain of a second voltage supply VDD. Output voltage level shiftingstage 302 is coupled to the input stage 301 receiving a first invertedsignal indicated at a node OUT_HIGH and also providing an output signalindicated at a node OUT_LOW. The output signal OUT_LOW has a voltagelevel shifted value corresponding to the second voltage supply VDD and alogic value corresponding to the input signal IN.

In accordance with features and other advantages of the preferredembodiments, the first voltage supply VDD2 optionally has a voltagelevel higher than or lower than the second voltage supply VDD. With thefirst voltage supply VDD2 having a voltage level higher than the secondvoltage supply VDD, level shifter circuit 300 functions as a high-to-lowlevel shifter, shifting a voltage level of a logic signal from a highvoltage to a low voltage. With the first voltage supply VDD2 having avoltage level lower than the second voltage supply VDD, level shiftercircuit 300 functions as a low-to-high level shifter, shifting a voltagelevel of a logic signal from a low voltage to a high voltage.

Input stage 301 includes a pair of series connected PFETs 304, 306connected in series with a pair of parallel connected NFETs 308, 310.

PFETs 304, 306 and NFETs 308, 310 are between the first voltage supplyVDD2 and ground. A first inverter defined by PFET 306 and NFET 308receives the input signal IN and provides a first inverted signal at afirst node or net labeled OUT_HIGH. A node or net labeled A is indicatedat the drain source connection of PFETs 304, 306.

Input stage 301 includes a second pair of series connected PFETs 312,314 connected in series with a second pair of parallel connected NFETs316, 318. PFETs 312, 314 and NFETs 316, 318 are connected between thefirst voltage supply VDD2 and ground. A second inverter defined by PFET314 and NFET 316 receives the inverted input signal INBAR and providinga second inverted signal at a node or net labeled B.

Output voltage level shifting stage 302 includes a first inverterdefined by a series connected PFET 320 and an NFET 322 connected betweenthe second voltage supply VDD and ground. A second series connected PFET324 and an NFET 326 is connected between the second voltage supply VDD.The second inverted signal at net B is applied to the gate connection ofthe output stage inverter PFET 320 and NFET 322. The first invertedsignal at net OUT_HIGH is applied to the gate of PFET 324, and theinverted output of output stage inverter PFET 320 and NFET 322 isapplied to the gate of NFET 326.

Level shifter circuit 300 includes a coupled network generallydesignated by the reference character 350 including a coupled networkinput stage generally designated by the reference character 351operating in a domain of the first voltage supply VDD2 receiving aninput signal at an input labeled IN and an inverted input signal at aninput labeled INBAR. Coupled network 350 of level shifter circuit 300includes a coupled network output voltage level shifting stage generallydesignated by the reference character 352 operating in the domain of asecond voltage supply VDD.

Coupled network output voltage level shifting stage 352 is coupled tothe coupled network input stage 351 receiving a first inverted signalindicated at node OUT_HIGH and also providing an output signal indicatedat the node OUT_LOW.

Coupled network input stage 351 includes a pair of series connectedPFETs 354, 356 connected in series with a pair of parallel connectedNFETs 358, 360. PFETs 354, 356 and NFETs 358, 360 are between the firstvoltage supply VDD2 and ground. A first coupled network inverter definedby PFET 356 and NFET 358 receives the input signal IN and provides afirst inverted signal at a first node or net labeled OUT_HIGH. A node ornet labeled E is indicated at the drain source connection of PFETs 354,356.

Coupled network input stage 351 includes a second pair of seriesconnected PFETs 362, 364 connected in series with a second pair ofparallel connected NFETs 366, 368. PFETs 362, 364 and NFETs 366, 368 areconnected between the first voltage supply VDD2 and ground. A secondinverter defined by PFET 364 and NFET 366 receives the inverted inputsignal INBAR and providing a second inverted signal at a node or netlabeled F.

Coupled network output voltage level shifting stage 352 includes a firstinverter defined by a series connected PFET 370 and an NFET 372connected between the second voltage supply VDD and ground. A secondseries connected PFET 374 and an NFET 376 is connected between thesecond voltage supply VDD. The second inverted signal at net F isapplied to the gate connection of the output stage inverter PFET 370 andNFET 372. The first inverted signal at net OUT_HIGH is applied to thegate of PFET 374, and the inverted output of output stage inverter PFET370 and NFET 372 is applied to the gate of NFET 376.

Input stage 301 and first output voltage level shifting stage 302 of thelevel shifter circuit 300 generally are functionally identical to thecoupled network input stage 351 and coupled network output voltage levelshifting stage 352.

Operation of the level shifter circuit 300 may be further understood asfollows. With a high or one level signal on the input IN and a low orzero level signal on the input INBAR, respective net A and net E beingthe drain of respective PFET 304, 354 is pulling high compliment of therespective source connected to the first power supply VDD2. Net B outputof inverter PFET 314 and NFET 316 gates PFET 304, NFET 310, PFET 320,and NFET 322, pulling in the direction of the input signal IN, whileconnected to the drains of NFETs 316, 318 and PFET 314. Similarly net Foutput of inverter PFET 364 and NFET 366 gates PFET 354, NFET 360, PFET370, and NFET 372, pulling in the direction of the input signal IN,while connected to the drains of NFETs 366, 368 and PFET 364. The inputsignal IN is applied to the gates of respective inverter PFET 306 andNFET 308, and inverter PFET 356 and NFET 358 each inverting the inputsignal, and maintaining a high level at output net OUT_HIGH as dictatedby the power supply VDD2 on source of PFET 304, 354.

This inverted signal at output net OUT_HIGH is maintained by being tiedto the gates of PFETs 324, 312 and NFET 318, and PFETs 374, 362 and NFET368. Respective net C, net G provides respective drain source connectionfor PFETs 312, 314 and PFETs 362, 364 respectively, following in thedirection of the inverted input signal INBAR. The inverted input signalINBAR is applied to the respective second inverter PFET 314, NFET 316and second inverter PFET 364, NFET 366 and is inverted as identified byrespective net B, net F and then shifted down to the target VDD by therespective output stage inverter PFET 320, NFET 322, and coupled networkoutput stage inverter PFET 370, NFET 372. The level shifter signal isnow held low and maintained by respective NFET 326, NFET 376. PFETs 320,324, NFETs 322 and 326, and coupled network PFETs 370, 374, NFETs 372and 376 respectively shift this signal to the shifted voltage level.

FIG. 4 illustrates exemplary operation of the level shifter circuit 300in accordance with the preferred embodiment, where the first voltagesupply level VDD2 in this case is 1.3V and is shifted up to the secondvoltage supply level VDD which is 1.95V. In FIG. 4, time is shown innanoseconds along the horizontal axis and voltage is shown along thevertical axis in volts (V). An exemplary input signal is indicated by INand an exemplary output signal of the level shifter circuit 300 at nodeOUT-LOW is indicated by OUT-LOW.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

1. A voltage level shifter circuit for shifting a voltage level of alogic signal from a first voltage to a second voltage comprising: aninput stage operating in a domain of a first voltage supply receiving aninput signal; said input stage including a first inverter receiving saidinput signal and providing a first inverted signal; and an outputvoltage level shifting stage coupled to the input stage, said outputvoltage level shifting stage operating in a domain of a second voltagesupply, and providing an output signal having a voltage levelcorresponding to said second voltage supply and a logic valuecorresponding to said input signal.
 2. A voltage level shifter circuitas recited in claim 1 wherein said first voltage supply is a highervoltage than said second voltage supply.
 3. A voltage level shiftercircuit as recited in claim 1 wherein said first voltage supply is alower voltage than said second voltage supply.
 4. A voltage levelshifter circuit as recited in claim 1 wherein said output voltage levelshifting stage providing a second output signal having a voltage levelcorresponding to said first voltage supply and a logic valuecorresponding to said first inverted signal.
 5. A voltage level shiftercircuit as recited in claim 1 wherein said output voltage level shiftingstage shifts a voltage level of said input signal from a high to a lowoperating voltage.
 6. A voltage level shifter circuit as recited inclaim 1 wherein said output voltage level shifting stage shifts avoltage level of said input signal from a low to a high operatingvoltage.
 7. A voltage level shifter circuit as recited in claim 1wherein said level shifter circuit enables high frequency operation in aselected GHz frequency range.
 8. A voltage level shifter circuit asrecited in claim 1 wherein said input stage includes a second inverterreceiving an inverted input signal and providing a second invertedsignal.
 9. A voltage level shifter circuit as recited in claim 8 whereinsaid input stage includes a first transistor coupled between the firstvoltage supply and the first inverter, said first transistor receives acontrol input of the second inverted signal.
 10. A voltage level shiftercircuit as recited in claim 9 wherein said input stage includes a secondtransistor coupled between the first voltage supply and the secondinverter, said second transistor receiving a control input of the firstinverted signal.
 11. A voltage level shifter circuit as recited in claim10 wherein said output voltage level shifting stage includes a firstinverter, said first inverter of said output voltage level shiftingstage is coupled between the second voltage supply and ground, and saidsecond inverted signal is applied to said first inverter of said outputvoltage level shifting stage.
 12. A voltage level shifter circuit asrecited in claim 11 wherein said output voltage level shifting stageincludes a series connected P-channel field effect transistor (PFET) andan N-channel field effect transistor (NFET) connected between saidsecond voltage supply VDD and ground.
 13. A voltage level shiftercircuit as recited in claim 12 wherein said first inverted signalprovides a gate signal to said PFET of said output voltage levelshifting stage, and an output of said first inverter of said outputvoltage level shifting stage provides a gate signal to said NFET of saidoutput voltage level shifting stage.
 14. A voltage level shifter circuitas recited in claim 13 wherein each of said first inverter and secondinverter of said input stage and said first inverter of said outputvoltage level shifting stage includes a series connected PFET and NFET,said series connected PFET and NFET having a common gate input.
 15. Avoltage level shifter circuit as recited in claim 1 further includes acoupled network, said coupled network is substantially functionallyidentical to said input stage and said output voltage level shiftingstage.
 16. A voltage level shifter circuit as recited in claim 15wherein said coupled network includes a coupled network input stageoperating in a domain of said first voltage supply receiving said inputsignal; said coupled network input stage including a first couplednetwork inverter receiving said input signal and providing said firstinverted signal; and a coupled network output voltage level shiftingstage coupled to said coupled network input stage, said coupled networkoutput voltage level shifting stage operating in a domain of said secondvoltage supply, and providing said output signal having said voltagelevel corresponding to said second voltage supply and said logic valuecorresponding to said input signal.
 17. A voltage level shifter circuitfor shifting a voltage level of a logic signal from a first voltage to asecond voltage comprising: an input stage operating in a domain of afirst voltage supply receiving an input signal; said input stageincluding a first inverter receiving said input signal and providing afirst inverted signal, a second inverter receiving an inverted inputsignal and providing a second inverted signal; and an output voltagelevel shifting stage coupled to the input stage, said output voltagelevel shifting stage operating in a domain of a second voltage supplyand providing an output signal having a voltage level corresponding tosaid second voltage supply and a logic value corresponding to said inputsignal; and said output voltage level shifting stage including a firstinverter, said first inverter of said output voltage level shiftingstage coupled between said second voltage supply and ground, and saidsecond inverted signal is applied to said first inverter of said outputvoltage level shifting stage.
 18. A voltage level shifter circuit asrecited in claim 17 wherein said output voltage level shifting stageincludes a series connected P-channel field effect transistor (PFET) andan N-channel field effect transistor (NFET) connected between saidsecond voltage supply VDD and ground.
 19. A voltage level shiftercircuit as recited in claim 18 wherein said first inverted signalprovides a gate signal to said PFET of said output voltage levelshifting stage, and an output of said first inverter of said outputvoltage level shifting stage provides a gate signal to said NFET of saidoutput voltage level shifting stage.
 20. A voltage level shifter circuitas recited in claim 17 further includes a coupled network, said couplednetwork being substantially functionally identical to said input stageand said output voltage level shifting stage.